Furnace



FURNACE Filed Feb. 19, 1930 2 Sheets-Sheet 1 g mT C. A. DUTTON Dec- 6,1932.

FURNAGE Filed Feb, 1.9. 1930 2 Sheets-Sheet 2 www Patented Dec. 6, 1932UNITED STATES PATENT QFF'ICE Appliation led February 19, 1930. Seria-1N0. 429,482.

Other objects of the' invention and the.

This invention relates to furnaces, particularly to those of the typeused in the art of burning enamel ware, wherein 'the furnace isconstructedin the form of a 'long corridor, closed at one end, throughwhich the work is carried by a conveyor arranged in the form of a U. Theentrance and exit mouth are side by side at one end of the corridor, theheating chamber being at the closed end which is remote from the mouth,and the section between the heating chamber and the mouths constitutinga heat interchange wherein the outgoing work gives oifheat to theincoming work while both are' moving slowly along the substantiallyparallel legs of the U-shaped track. For convenience such a furnace ishereinafter referred to 'as U-shaped.

A problem of great importance to be solved in the economical operationof such furnaces is the retention of heat.- A further problem is toaccomplish effective interchange of heat between the hot outgoing andcold incoming ware, whereby the former is gradually cooled down beforepassing into the outside air, and the heat instead of being wasted isemployed to bring the latter by gradual increase as near as may be tothe temperature of the heating chamber, thereby reducing the heatconsumption as well as producing a more perfect finish of the enamel bythe avoidance of sudden changes in temperature.

Among the objects of this invention is the provision of relativelysimple and effective means for solving the problems outlined above, andparticularly the provision of air screens for preventing the escape ofheat from the furnace doorways which will not interfere with theconveyor operation and which will materially aid the heat interchangeprocess. Another object is to promote the heat interchange by inducing atransverse circulation of air in the heat interchange chambers so thatthe air which passes over the outgoing hot ware will contact with theincoming cooler ware substantially opposite, and with the result thatextreme difference in temperature between the opposite pieces of burnedand unburned work at any point along the conveyor will be materiallyreduced.

method of securing the same will appear from the followingspecification, which, taken in conjunction with the accompanyingdrawings, sets forth a preferred form of practical application of theprinciples of my invention. It is to be understood, however, that thespecifications and vdrawings are by way of example and not limitation,and that other embodiments are within the purview of the invention.

Fig. 1 is adiagrammatic plan view of a furnace showing the applica-tionof various features of my invention thereto; Figs. 2, 3 and 4 are,respectively, the front and side views and top plan View of a heatinterchanging air screen apparatus, the front and side views beingpartly sectional and partly elevational; Fig. 5 is a partial-detail ofthe conveyor and hood, approximately on the line 5 5 of Fig. 3; Figs. 6,7 and 8 are respectively front, side and top views of a modified form ofapparatus for producing an air screen, corresponding to Figs. 2, 3 and4, respectively, and Fig. 9 is a view on the line 9 9, Fig. 1, showingthe circulation of air within the hea-t interchange chamber.

Referring to Fig. 1, the furnace will ordinarily be builtin the form ofa long chamber surrounded by suitable refractory walls l, and having aheating chamber 2, closed by the end wall 3, and theheat'interchangerchamber 4, usually much longer than the heating chamber; the relativeproportions being in accordance with the nature of the treatment forwhich the furnace is designed. A pillar 5 divides the furnace mouth intotwo doorways 6 and 7. The work, generally indicated by the referencecharacter 8, illustrated as being carried through the furnace by acontinuous conveyor system 9 of the trolley type, and convenientlycomprising a chain 10, (Fig. 3), driven in the direction of the arrowsin Fig. 1 by suitable means not shown and not constituting a part of myinvention. The work is suspended from the conveyor `through rods 11which depend through a U- shaped slot in the top of the furnace. Shoeplates 13 slide along suitable tracks and cover the top of the slot andprevent the escape of heat therethrough. The shoe plates overlaplongitudinally and are moved by the rods in their travel around thefurnace. The shoe plates are free to move up and down on the upper partof the rods 11, bein supported by collars 11 on the rods when o thetracks. The shoe plates are raised from and lowered to the collars 11near the open end of the furnace by shoe plate guides 12 which havedonwardly inclined ends extending beyond the front wall of the furnace.The furnace and conveyor are of a type more fully described in thecopending application of Leo W. Manion, Serial No. 364,477, tiled Mayth, 1929, and will not be further described herein.

Referring now to Figs. 2, 3, 6 and 7, the doorwa s 6 and 7 are open. Theprevention of dra ts of air through these doorways, which would causeloss of heat, is accomplished by air screens, each consisting preferablyof an upward blast of air across the entire width lof each opening, asindicated bythe arrows with solid shafts. In the form shown b Figs. 2and 3 the air discharged from a lower 15, suitably located outside thefurnace, is directed into a discharge duct 17 placed against the frontwall of the furnace below the doorway 7 and having a suitable blastnozzle or slot 18 to direct the air upward in a thin stream the fullwidth of the doorway. A hood 19 is secured across the top of thedoorway, and is of sufficient width and thickness to collect the airstream. This hood, to be described in greater detail below, connects atone end with a conduit 20 which leads to the suction side of a secondblower 21, the blast from which discharges through a discharge duct 22and nozzle or slot 23 bearing the same relation to the doorway 6 thatthe duct 17 and nozzle 18 do to the doorway 7. Thus a similar upwardairf screen is created at the doorway 6, this screen being collected bya hood 24 and returned by a conduit 25 to the first blower 15.

Heretcfore work coming out of the doorway 7 was at about 400 to 700 F.The air screen, moving upward, in conjunction with the natural rising ofthe air from the hot ware, carries away a considerable quantity of thisheat, which is in turn imparted to the work entering the furnace throughthe air screen in front of the doorway 6.

Figs. 6, 7, and 8 represent a modified form of air screen wherein asomewhat simpler arrangement is used. In this form air from the blowerdivides in the discharge conduit 31 and is driven up through two nozzles32 corresponding to the nozzles 18 and 23, across the doorways 6 and 7and collected in the respective hoods 33, from each of which it isreturned by a common conduit 34 to the suction side of the blower 30. Itis apparent that by this course of circulation the air which is drivenpast the hot work in the doorway 7 becomes mixed in the conduit 34 withthe I cooler air from the doorway 6, but that as soon as circulation haskept up for av few minutes the average will become greater than thetemperature of the ingoin work, although it will always be less thanthat of the outgoin so -that a ver material heat interchange wi l beproduced y this form of air screen also.

I regard the construction of the intake hood as shown at 19, 24 and 36as one of the outstanding features of my invention. Heretofore screenshave been constructed with separate intake or discharge pipes andpositioned near the top of the doorway on opposite sides of the path ofthe conve or rods and on opposite sides of the slot in the roof of thefurnace whereby the screen has been in effect divided in two parts atthe top with a consequent loss in etiiciency. My hood construction isbased on the theory that kthe air of the screen having passed upwardlyacross the doorway of the furnace, can best be directed laterally acrossthe path of the conveyor rods instead of being carried upwardly individed paths on opposite sides thereof.

To this end the top wall 51 of the hood (see Fig. 5) lies substantiallyhorizontal, although preferably inclined upwardly in the direction ofthe flow of air and underlies and closely contacts with the shoe plateguides 12. It will be seen particularly from Fig. 5 that the shoe plates13 overlying the guides 12 form with the top wall 51 a continuous closedtop wall for the hood, whereby all of the upwardly flowing air in thescreen is diverted and carried laterally under the top wall into theintake conduits and thence to the blower. The inner or back side wallsof the hood may comprise or lie adjacent to the front walls of thefurnace so that the inner wall of the hood is continuous except for theslot in the roof of the furnace, which however, is wholly covered by theshoe plates, as shown in Fig. 4.'

The front wall of the hood extending as it does about a foot from thefront wall ofl the furnace and parallel thereto is divided by a slo't 53longitudinally aligned with the major slot in the roof of the furnace topermit the passage of the work carrying rods 11. The shoe plate guides12 (see Figs. 3 and 4) extend beyond the front wall of the hood and arethence inclined downwardly as at 12', whereby they raise and lower theshoe plates as they move toward or away from the furnace.

/Those skilled in the art will appreciate that this hood constructionwill gather and receive all of the upwardly flowing air of the screenand conduct it without loss to the blower whence it is re-directedacross the opening. Such means as bale plates 52 (see Figs. 2 and 6) maybe built into the hoods adjacent the intake conduits for the purpose ofbalancing and proportioning the ilow throughout the body of the hood.The essential characteristic of the hood construction is that the flowis directed laterally across the path of the conveyor rods under acompletely closed top wall, whereby the screen is not divided or Atinualeddy, as represented diagrammatically by the circle of arrows 39 in Fig.9.

A suitable apparatus to accomplish this 1s illustrated in Figs. 1 and 9,the arrangement there shown comprising a series of openings 40, 41arranged in pairs near opposite sides of the furnace Hoor, beneath thepaths of the work, with preferably the blast opening under the hotoutgoing work 8A to assist the rising of the air due to the heat. Thecool incoming work is represented at 8B. To avoid the creation ofundesirable air currents in the heating chamber 2 these pairs ofopenings should preferably be placed in the forward half of the chamber4 longitudinally spaced at intervals of about ten feet. Each pair ofopenings is intended to provide an air current which will have aninducting effect on the generalbody of airinthe forward part of theinterchange chamber, and the number of pairs of openings is proportionedto the length of the general eddy desired.

In detail the openings 40 and 41 of each `pair (see Fig. 9) areconnected to the blast and-suction sides respectively of blowers 42through conduits or passageways 43 and 44. The blowers and motorstherefor are preferably located outside the furnace and the conduitsorpassageways are preferably built into the floor and foundation.

The speed of the blowers may be controlled in any suitable manner andone of the advanta-ges of this arrangement is that the rate at which thecold ware is dried and the hot ware cooled can be accurately controlledby regulating the speed of the blower motors. I provide slide valvesV'for controlling the flow through the conduits leading to or from theblowers. Heretofore the rate of coolin and drying has largely beencontrolled only by the speed of the conveyor upon which the ware iscarried with the result that the fura `nace capacity has been greatlylimited. For

instance, if it were desired to force a furnace by increasing the speedof the conveyor fully laden with ware two difficulties would ensue. Onone hand, the work might be heated and cooled too rapidly with theresult of imperfection in the finished product and on thel other hand,the ware would come from the furnace at abnormally high temperatureswith the resulting waste in heat. According to the precepts of thisinvention, I am able to transfer the heat from the hot to the coldV wareso that as the conveyor may be speeded without the heretofore consequentloss of heat. Furthermore, this transfer of heat from hot to cold ware,effects an even though more rapid drying of the cold incoming ware withthe result that the incoming work is thoroughly dried before enteringthe burning chamber proper. I wish also to point out that the blowers 42in effecting internal circulation of air in the preheating and coolingchamber set up, a condition which in itself has an effect comparable tothat: of the air screen at the furnace door. The rotation of4 air withinthe preheating and cooling chamber acts in conjunction with the airscreen and aids it in preventing the natural longitudinal flow of airinto the body of the screen, there is a natural outflow of hot air andinflow of cold air through the furnace doors which results in theaddition of fresh air to the furnace atmosphere and the consequentdisplacement of moisture and other gaseous products incident to theburning of the ware. Were the air screen eficient and were there noleaks in the furnace, the furnace atmosphere would acquirecharacteristics vastly different from fresh air. I bel'eve such acondition to be not necessarily desirable in all instances and thereforeprovide means for controlling the volume of air circulated in the screenwhereby the efficiency ofthe screen may be controlled and whereby thenatural flow of air or gas into or out of the furnace doors may bepermitted within controlled limits.

Thus slide valves VV are provided in the conduit 31 and in the conduits17 and 22, whereby the How of air in the screen may be controlled. Iappreciate that suitable electrical control for the blower motors mightbe substituted but whatever the means of control, it is my object toprovide means for controlling the volume of air circulated in the g'screen so that the efhciency of the screen as a means for preventing thenatural circulation of air into and out of the furnace must be variedwith the result that the character of the atmosphere in the furnace maybe controlled.

Having described certain preferred embodiments and applications of myinvention, it is to be understood that I do not limit myself to theforms shown but that a variety of other forms may be used in practice,so long as they fall within the scope delimited by the following claims.For example, although the circulating medium is described and claimed asatmospheric air, the invention is equally applicable to the use of someother gaseous circulating medium, which might conceivably be differentfrom the general atmosphere of the furnace and lant. lt is my intentionthat the Word air in the subjoined claims be interpreted with thebreadth of meaning above indicated.

I claim:

l. Screens for entrance and exit openings of a heat-treating furnacethrough which work is passed in a continuous stream comprising a singlemovino' body of air passing successively across said openings bycontinuous movement.

95A heat exchange Vmethod operable in conjunction with a continuousconveyor furnace which comprises the continuous movement of a body ofair in curtain form across the mouths of such furnace in sequence fromdischarge mouth to loading mouth, whereby the same air abstracts heatfrom material leaving and applies it to material entering the furnace.

3. The method of forming air screens simultaneously across the loadingand discharge openings of a continuous conveyor furnace which comprisesdriving air upwardly through restricted discharge -means disposedacrossthe bottom of one opening, collecting the same air across theentire width of the top of the same opening, then passing the same airin similar manner across the other opening from the bottom to the topthereof.

4. The method of forming air screens simultaneously across the loadingand discharge openings of a continuous conveyor furnace which comprisesdrivingI air upward ly through restricted discharge means disposedacross the bottom of one opening, collecting the same air across theentire width of the top of the same opening, then passing the same airin similar manner across the other opening from the bottom to the topthereof and returning the same air to the point of beginning in acontinuous closed pat Y 5. Means for forming heat-exchanging' airscreens across the incoming and outgoing mouths of a continuousheat-treating furnace comprising a single hood across the full width ofthe top of each mouth, a blast orifice across the bottom of .each mouth,a suction connection at one side of each hood, air impellingl meanscommon to both furnace mouths adapted to draw air from both suctionconnections and discharge it to both l blast orifices, allsimultaneously and con- 4comprising a lsingle hood across the full widthof the top of each mouth, a blast orifice across the bottom of eachmouth, a suction connection at one side of each. hood, a separate airpassage from each hood suction connection to the blast orifice of themouth, and air impelling means in each of said passages.

7 The method of heat interchange in a U- shaped enameling furnaceprovided with a continuous conveyor which comprises setting up acirculation of air therein about an axis parallel to the conveyor pathsand of substantially permanent location longitudinally of the furnace.

8. In a U-shaped continuous conveyor heat treating furnace, heatretaining and interchanging means comprising means for inducing asubstantially transverse rotation of air in the heat-interchange chambercomprising a plurality of streams of air moving with the same directionand speed across three sides of said chamber.

9. In a U-shaped continuous conveyor heat Iing a plurality of streams ofair moving with the same direction and speed across three sides of saidchamber.

10. In a U-shaped continuous conveyor heat treating furnace, heatretaining and interchanging means comprising means for causing asubstantially non-spiral circulation of air around an axis longitudinal0f the heat-interchange chamber, said means comprising a plurality ofopenings arranged in pairs, each pair near opposite sides of one face ofsaid chamber, a blast and a suction means connected respectively withone of the opposed openings of each pair, a conduit connecting each pairof openings, and a. circulating fan in each conduit, all of said fansbeing arranged to move air in the same directional sense.

11. In combination with a continuous-process heat treating furnace ofthe type having work passing doorways always open, an exterior overheadconveyor, work-supporting rods depending from said conveyor, and a slotfor the passage of said rods, air screen means across said doorways eachcomprising an uninterrupted hood across the top of said furnace, a slotthrough said hood aligned with said furnace slot, covering means for thetop of said hood comprising a plurality of plates moved by said rods,said plates overlapping and resting upon the top edges of the slot andoverlapping one another endwise air discharging means across the bottomof the furnace below and of equal length with said hood. and means forcausing a continuous thin blast of air between said discharge means andsaid hood across the full width thereof.

12. An air screen hood for a conveyor furnace opening comprising sides.a top, and an outlet at one end, two opposite sides being a conveyorfurnace comprising two sections forming an operative unit, said sectionsbeing spaced apart to leave a slot for the passage of conveyor elements,shoe plates carried by said elements covering the top of said slot, saidshoe plates mutually overlapping longitudinally and forming a part ofthe hood top.

14. A furnace having\ entrance and exit openings and through which workis continually passed and in which the work is raised to a maximumtemperature in the course of its movement between the entrance .and exitopenings having in combination means for causing a forced flow offurnace atmosphere past thehot outgoing work and thence into contactwith the cool incoming work whereby the incoming work is preheated bythe heat from the out oing work and means for directing blasts o airacross said intercepting the paths i of both streamsof ware by a singlemoving body of air passing suclesslvely across said ware in a continuouspat Y 19. The method of heat treating ware which `consists inabstracting the heat from ware after undergoing the process of heattreatment and creatinga positive air circulation adapted to conduct theabstracted heat to other ware undergoing the process of heat treating.

20. In a furnace for heat treating ware, means for conducting incomingand outgoing ware in adjacent streams, means forv creating an air screenin said furnace, said air screen lcomprising a body of air in constantcirculation, said body including two, separate sheet like sectionsmoving upwardly toward the upper confines of said furnace, oneintercepting the path of incoming ware and' the other intercepting thepath of the outgoing ware. 1

In testimony whereof I hereunto aillx my signature this 16th day ofFebruary, 1930.

CHAUNCEY ARNOLD BUTTON.

entrance and exit openings for preventing the natural eilux o warmfurnace atmosphere and influx of cool outside atmosphere.

15. A furnace according to claim 14 wherein means` are provided forcontrolling the rate of said forced flow of furnace atmosphere wherebythe rate of preheating the incoming work ma be varied. 1 y

16. A rnace according to claim 14 wherein means are provided forcontrolling the volume of the blast directed across said entrance andexit openings, whereb ascertainable amounts of natural eiux an inflowmay be permitted throu h said o nings. 4

17. A U type rnace o the class described having a burning chamber at theclosed end i and having entrance and exit openings at the opposite endand' having a preheating and cooling chamber between said burningchamber and said openings, andhaving -1n combination means forcontinuously conveying work through said furnace and throu h saidopenings in oppositely moving and adjacent paths at least in saidpreheating and cooling chamber, means for causing a circulation offurnace atmosphere about the longitudinal axis of said reheatin andcooling chamber for transferring heat rom het to cold work and means forcausing a stream of air to flow across said openings to restrict thenatural flow of air or gas into and out of said furnace through said o18. The metlie which consists in causing the incoming and outgomg wareto pass in adjacent streams and od of heat treating ware

